Directional coupler (2 Students)

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Lester Ford
6 years ago
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Directional coupler (2 Students) The goal of this project is to make a 2 by 2 optical directional coupler with a defined power ratio for the two output branches.

1 Directional coupler (2 Students) The goal of this project is to make a 2 by 2 optical directional coupler with a defined power ratio for the two output branches. The directional coupler should be optimized for the operating wavelength of λ = 1550 nm. In a first directional coupler design, the output power should be equally split between the two arms (50/50) with minimal overall losses. In a second design, the output splitting ratio should be 90/10. The general geometry of a directional coupler is shown in Figure 1. Tasks 1. Literature search. The first task is to familiarize with the theory behind directional coupling. This should give you an idea of the geometry that a directional coupler should have, and which parameters are critical to achieve the specified goals. 2. Single mode waveguide. Directional couplers are based on guided wave, Si/SiO 2 waveguides for this project. Therefore, the design of a single mode Silicon waveguide (at λ = 1550 nm) using the 1D eigenmode solver of COMSOL (Boundary Mode Analysis) is the first design goal. The material of the core is Silicon, while the cladding is SiO Bending losses. Bending of the waveguide is required for the coupling section. The bending should be optimized for the smallest radius with a maximum loss per pending. The structure can be symmetric, so only one bending radius optimization is needed. a. NOTE: if you want, you could do asymmetric structure, but that would require 2 bend loss calculation. However, if you have an idea and good reason to do it, you are welcome to try! 4. Coupling section. The entire structure should be modeled, and the coupling section should be optimized for the specified power ratios. a. NOTE: Sweeping the length of the coupling section and/or distance between the waveguides and plot the two output power can reveal the ideal coupling section parameters. 5. Convergence. The final structure should be tested with smaller mesh size /10 directional coupler. After the convergence test, the design should be adapted for the power ratio in the two arms to be 10%/90%. 7. Report and presentation. The results of the project should be summarized in the form of a B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley.

In this configuration, rings with varying radii in series have to form an add/drop circuit with 50/50 power distribution. Fig. 2 shows an implementation example.

2 Ring Resonator (2 Students) The goal of this project is to design and simulate a Silicon-on-Insulator optical ring resonator. The device should act as a notch filter at the operating wavelength of 1550nm. In a second step, a cascaded multi ring resonators device has to be designed. In this configuration, rings with varying radii in series have to form an add/drop circuit with 50/50 power distribution. Fig. 2 shows an implementation example. The general geometry of an add/drop ring resonator and cascaded resonators are shown in Figure 1. Milestones 1. Literature search. The first task is to familiarize with the theory behind ring resonators. The most important is to answer to questions of which parameters are playing the crucial roles. You should first calculate the ring parameters (radius) for the required resonance wavelength. 2. Single Mode Waveguide. Design a single mode Silicon waveguide (at λ = 1550 nm), using the 1D eigenmode solver of COMSOL (Boundary Mode Analysis). The material of the core is Silicon, while the cladding is air. 3. Ring Resonator. Based on your calculation, the ring radius has to be optimized to have resonant behavior at 1550nm and minimal bending losses. 4. Single Ring Filter. The ring radius has to be further optimized not only to show resonance at 1550nm, but also have a Q factor and a FWHM of about and 10nm, respectively. Additionally, the coupling between the waveguide and ring resonator has to be such that the extinction ratio is above 20dB. 5. Cascaded Structure. An add/drop filter design with cascaded ring resonators in series has to be designed. The power distribution should be optimized to 50/50 at the two forward outputs. 6. Report and presentation. The results of the project should be summarized in the form of a B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley.

Delay Interferometer (2 students) The goal of this project is to design and simulate a delay interferometer based on a Mach-Zhender configuration for the purpose of verifying the coherence of a light

3 Delay Interferometer (2 students) The goal of this project is to design and simulate a delay interferometer based on a Mach-Zhender configuration for the purpose of verifying the coherence of a light source. This project can be divided into two main work. One is the design and optimization of the coupling section, which is the splitting and interference section of the interferometer. Second, an asymmetric delay line should be designed and optimized to induce a π-shift in one arm of the interferometer. Both designs should have minimal losses and optimized for the operating wavelength of 1550nm. The general geometry of a Mach- Zhender interferometer is shown in Figure 1. Task Milestones 1. Literature search. The first task is to familiarize with the theory behind Delay Interferometers, especially the Mach-Zhender configuration. Important is also the theory about directional coupling. You can use theory to calculate the delay line length to achieve a specific relative phase shift. 2. Single mode waveguide. Next is to design a single mode Silicon waveguide (at λ = 1550 nm), using the 1D eigenmode solver of COMSOL (Boundary Mode Analysis). The material of the core is Silicon, while the cladding is air. In both, the coupling scheme and the delay line, the waveguide dimension should be the constant. 3. Splitting scheme. A splitting scheme based on a directional coupler should be implemented with a splitting ratio of 50/50. The coupling length can be reduced by optimizing the waveguide separation. This reduced the overall dimension of the device. Similarly, the bending curvature should be optimized for low bending with minimum losses. 4. Interference scheme. For the coupling (interference), two options are possible. First option, you can use the same scheme as used for your splitting scheme. Based on the interference, the power will be split between the two outputs. Second option, you design a multi-mode interferometer (MMI), such as to observe interference behavior on a single output (a bit more effort, but you can collaborate with the MMI group). 5. Symmetric interferometers. In a first step, design and optimize the delay line with symmetric dimension. This step is useful to optimize the bending radius of the two arms. Note that, this should result in a constructive interference at the output. 6. Asymmetric Delay line. Based on your calculation, optimized the delay line length for a π-shift (wavelength of 1550nm). Do not forget the additional phase delay in the reference line! 7. Putting the things together. In the last step, the entire structure has to be assembled, and the π-shift should be verified by calculating the extinction ratio on the output lines (> 10dB). If possible, make a sweep of the delay line. With this, you can plot the output power as a function of the relative phase shift. 8. Convergence. The final structure should be tested for the mesh size. 9. Report and presentation. The results of the project should be summarized in the form of a

4 B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley.

5 Bragg Mirror (2 Students) of this project is to design a Bragg mirror with specified reflectivity R = 99% at the operating wavelength of λ = 1550 nm. In the first design, only one wavelength will be considered. In the second run, a range of wavelengths will be considered, so that 3dB (half of the power) reflectivity can be achieved over range of wavelengths. The general geometry of a Bragg reflector is shown in Figure 1. Milestones 1. Literature search. The first milestone is to familiarize with the theory behind the Bragg mirror. The most important is to answer to questions which parameters are playing the crucial role. 2. Single mode waveguide (COMSOL). The following milestone is to design a single mode Silicon waveguide (at λ = 1550 nm), using the eigenmode solver of COMSOL. The material of the core is Silicon, while the cladding is SiO Infinite Bragg mirror. The next milestone is to perform theoretical calculations of the infinite Bragg mirror (2 physical dimensions are infinite), so the starting design points (number of periods, filling factor and period) for COMSOL simulations could be chosen (see Figure 1). 4. COMSOL simulation of the mirror. Once the initial parameters are known, the Bragg mirror should be simulated in COMSOL with the following goals: a. Reflection coefficient of 99% for λ c = 1550 nm b. Reflection coefficient >3dB for λ c ± 100 nm 5. Convergence test. The results should be tested for different mesh sizes. 6. Report and presentation. The results of the project should be summarized in the form of a Λ B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley. d Si Figure 1: The Bragg mirror. The most important design parameters are the period (Λ), then thickness of the Si part (dsi), as well as filing factor ff = dsi/λ and number of periods N.

Multimode Interferometer (2 Students) of this project is to design a multi-mode interferometer (MMI) with specified output coupling operating at the wavelength of λ = 1550 nm.

6 Multimode Interferometer (2 Students) of this project is to design a multi-mode interferometer (MMI) with specified output coupling operating at the wavelength of λ = 1550 nm. In the first design, a 1x2 configuration is considered with an output ratio of 50:50. In the second run, the MMI should be optimized for an output ratio of 10:90. The general geometry of a MMI is shown in Figure 1. Task 1. Literature search. The first task is to familiarize with the theory behind the MMI. The most important is to answer to questions which parameters are playing the crucial role. Based on the theory you can estimate initial parameters. 2. Single mode waveguide (COMSOL). The following task is to design a single mode Silicon waveguide (at λ = 1550 nm), using the 1D eigenmode solver of COMSOL (Boundary Mode Analysis). The material of the core is Silicon, while the cladding is SiO MMI. Based on the estimated dimensions, you can design and simulate the MMI. From this point you can optimize the structure for a 50/50 coupling ratio. Make sure the overall losses are be below 1dB and minimize the reflections. a. Note. You can start by simulating a long interference section, and optimize only the width of the MMI. This allows you to then clearly see the 50/50 and 90/10 interference lengths. b. Note. You can use tapers to reduce scattering losses and reflection. 4. Convergence test. The results should be tested for different mesh sizes. 5. Second MMI. The 1x2 MMI should be optimized for the new goal: a. Output ratio of 10:90 for λ c = 1550 nm b. Overall losses below 1dB 6. Report and presentation. The results of the project should be summarized in the form of a Figure 1 Multimode interferometer 1x2 configuration. B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley.

Numerical Analysis and Optimization of a Multi-Mode Interference Polarization Beam Splitter

Numerical Analysis and Optimization of a Multi-Mode Interference Polarization Beam Splitter Y. D Mello*, J. Skoric, M. Hui, E. Elfiky, D. Patel, D. Plant Department of Electrical Engineering, McGill University,